Sub-surface crack propagation analysis in hypoid gears

This paper proposes a numerical approach devoted to the investigation of the sub-surface crack propagation mechanism in gear pairs having crossing axis (i.e. hypoid gears). Starting from an accurate 3D description of the complex gear tooth geometry, a numerical analysis carried out by means of an advanced contact solver allows obtaining, over the entire meshing cycle, the contact pressure distribution and the displacement field in the un-cracked tooth. Then, such displacements are applied as boundary conditions to a second finite element model of the cracked zone, being the aim the stress intensity factors calculation for the modes I, II, III along the crack front. At this point it is possible to examine the crack growth mechanism: the maximum shear SIF range and the maximum tensile SIF range are computed and considerations about direction of crack propagation are drawn. As application of this approach, a circular sub-surface crack in a real hypoid gear of a truck differential transmission is analysed.